1. Field of the Invention
The present invention relates to an image capturing apparatus and a control method for the image capturing apparatus. In particular, the present invention relates to an image capturing apparatus that uses an image sensor composed of pixel units each provided with one microlens and a plurality of photoelectric converters and that achieves a focus detection function using a phase difference method, and to a control method for the image capturing apparatus.
2. Description of the Related Art
There are conventional techniques to acquire a signal for focus detection and an image signal for recording with the use of one image sensor (for example, see Japanese Patent Laid-Open No. 2007-325139). In an image capturing apparatus described in Japanese Patent Laid-Open No. 2007-325139, a plurality of photoelectric converters are arranged under one microlens. This image capturing apparatus conducts focus detection in accordance with a phase difference method using a signal acquired in response to luminous fluxes that have passed through areas of different exit pupils, and generates an image signal using the acquired signal. In this way, a signal for focus detection and an image signal for recording can both be acquired using one image sensor.
However, the technique described in Japanese Patent Laid-Open No. 2007-325139 has the following problems. Although signals for phase difference detection can be acquired by reading signals separately from the plurality of photoelectric converters, the acquired signals need to be added in order to generate the image signal. This addition increases the amount of noise and worsens the S/N ratio of the image signal. Furthermore, as the number of photoelectric converters provided for one microlens increases, the S/N ratio worsens.
In addition, Japanese Patent Laid-Open No. 2007-325139 describes switching between combinations of signals to be added among the photoelectric converters. However, there is a limitation on the combinations of signals to be added, thus resulting in the problem of reduced flexibility.